13. OXYGEN ISOTOPIC COMPOSITION OF INTERSTITIAL WATERS FROM
LEG 154: DETERMINATION OF THE TEMPERATURE AND ISOTOPIC
COMPOSITION OF THE GLACIAL OCEAN1

Daniel P. Schrag,2 Gretchen Hampt,3 and
David W. Murray4

ABSTRACT

Oxygen isotope measurements of interstitial waters from Ocean
Drilling Program Leg 154, sampled at high resolution from Sites
925 and 929, are used to reconstruct the oxygen isotopic
composition of deep water during the last glacial maximum (LGM).
The data from both sites show an increase with depth, predicted
by modeling the diffusion of water through the sediment, although
only data from Hole 925E are appropriate for calculating the
composition of seawater during the LGM. Using a numerical model
to simulate diffusion of water in the sediments, we obtained a
glacial-interglacial change in the of seawater at Site 925 of 0.8 ±
0.1. This implies that the bottom water at Site 925 cooled
by approximately 4°C during the LGM. Although these data from a
single site do not represent a global average, we suggest that
the substantial cooling of deep water at Site 925 is consistent
with a global average change in the of seawater of 1.0. This value is
within the limits imposed by the freezing point of seawater and
is more consistent with estimates of the of continental ice during the glacial
maximum. In addition, a lower contribution from ice volume to the
change in of
planktonic foraminifers allows for 1°-2° additional cooling in
the tropics during the LGM, partially reconciling the
foraminiferal oxygen isotope record of tropical sea surface
temperatures with estimates from Barbados corals and terrestrial
climate proxies.